Systems and devices using fluid pressure for lifting and holding position are known. These systems and devices typically include check valves, which prevent sudden and potentially damaging loss of pressure when the supply of pressurized fluid unexpectedly decreases or fails. Typically, the check valves are opened either by applying a lower pressure pilot fluid, or by applying manual pressure, sufficient to overcome the locking forces.
The amount of force required to open a check valve depends upon the area of the main check valve that is locked, and the magnitude of the pressure. For example, to unseat a main check valve having a 0.75 inch diameter, which is seated at a pressure of 100 psi, about 44 pounds of opening force must be applied. This opening force is more than a typical operator can apply, either manually or using a solenoid. Furthermore, the higher force on the main check seat imposes added wear and tear, which leads to reduced operating life. The requirement of large pilot pistons also increases the overall dimensions of the valve itself.
There remains a need for pilot operated check valves requiring reduced operating forces, which, in turn, will lead to increased operating life at higher pressures. There is also a need for pilot check valves having a more compact size.